Corrosion Properties of Laser-Welded Superaustenitic Stainless Steel Sandwich Structures

摘要

The localized corrosion behavior of laser spot-welded UNS N08367 superaustenitic stainless steel (SASS) in 0.6 M sodium chloride (NaCl) solution at ambient and elevated temperatures was investigated through a variety of approaches. Localized corrosion behavior was connected with laser weld microstructure using macro- and microelectrochemical characterization and exposure experiments conducted on laser-welded sheet over a range of weld input energies. Corrosion experiments were augmented by studies on closely related materials such as UNS N08366, UNS N08904, and UNS N08367 with different Cr, Mo, or N contents, used to mimic the Mo-rich and depleted regions of the laser weld microstructure of UNS N08367. In addition, complimentary studies were conducted on furnace heat-treated, resistance spot-welded, and laser-welded UNS N08367 SASS sandwich structures. Long-term furnace heat treatments resulted in subsequent degradation of corrosion resistance of the alloy. Good corrosion resistance was maintained in rapidly cooled laser welds owing to retention of a face-centered cubic (fcc) solid solution, minimization of Mo partitioning between dendritic and interdendritic regions in the solidified weld microstructure, and avoidance of detrimental phase precipitation. Significant dendritic undercooling and small dendritic tip radius are rationalized to contribute to the formation of weld dendrite cores and interdendritic regions with minimal Mo partitioning. High-energy laser spot-welded and bonded face sheet and truss core structures fabricated from UNS N08367 maintained good localized corrosion resistance owing to a minimization of Mo segregation and speculated minimal loss of N loss in the weld region. [PUBLICATION ABSTRACT]